I just found a cute little app for the iPad (and a companion driver for Windows) that turns the iPad into a second, external monitor for a Windows laptop (or desktop, I suppose).

There are a couple of these out there; I ended up getting MaxiVista for ten bucks.

It works nicely when both computers are on the same wired or wireless network. Still trying to sort out how to get it to work on an ad-hoc setup ... ie, where the wireless network is between the computer and the ipad only.